Here's a message I put together last year, when I was having intermittent problems with my coil. If anyone can find a source of genuine Bosch coils, please let me know ...
Digifant Ignition Coil, spark plug lead and rotor testing
There are a number of on-the-car, shade-tree
tests for your ignition coil, but to definitively determine whether your coil
is on the way out, the only proper coil test is with a multimeter. Why? Here's
the rundown:
Inside an ignition coil are two coils of wire
on top of each other. These coils are called windings. One winding is called
the primary winding, the other is the secondary. The primary winding gets the
juice together to make a spark and the secondary sends it out the door to the
distributor. Either one of these windings can go bad and cause your ignition
coil to fail.
Sometimes an ignition coil is bad, clearly
bad, as in it makes no spark at all. But if a coil is on the way out, but not
dead yet, it can make a weak spark that can cause the car to run rough or
wrong. By testing an ignition coil with a multimeter while it's disconnected,
you'll be using data and numbers to determine the health of the coil rather
than your eyeballs and dead reckoning.
We'll show
you how to test both the primary and secondary ignition coil windings using a
multimeter.
*You'll
need the resistance specifications for your specific coil in order to perform
this test. Consult your service manual for this information. The figures given
below are for the standard VW coil, PN 211 905 115 D.
The primary winding of your ignition coil
is the first to receive voltage from the battery. Find the resistance
specifications for your car's primary coil winding in your repair manual. Then
using a multimeter, place the leads on the smaller, outside poles if you have a
traditional round coil, or on the indicated poles if you have a newer enclosed
unit. If the reading is within the range indicated in your manual, your primary
winding is ok and you can go on to the secondary test. If it is even a little
out of spec, the coil should be replaced.
The secondary winding of your ignition coil delivers the spark to the
distributor to be sent to the spark plugs. If it's bad, you'll get a weak spark
or no spark at all.
To test
the coil's secondary winding, attach the test probes to the outer 12V pole and
the centre pole (where the main wire goes to the distributor). Determine the
resistance and check to see if it's within the range indicated in your repair
manual. If it is, your coil is up to the task. If it's even slightly out of
range, your coil should be replaced.
VW T3 coil;
If
an ignition coil fails completely, it will make no spark at all. But if it is
performing below par, it can make a weak spark that can cause the van to run
badly.
I
once tested three used VW coils in search of a good one. All would make the
engine run, but none of them were up to spec. The purchase of a new coil made a
noticeable difference.
The primary winding of the ignition coil is
the first to receive voltage from the battery when the ignition switch is
turned on, via terminal
15 (+).
Using
a multimeter, place the probes on the small outside wires (terminals 15(+) and
1(-). If the primary
resistance between the two is 0.5 to 0.8Ω, the primary winding is ok and you can go on to the
secondary test. If it is out of spec, replace the coil with the spare that you
always carry under the seat.
The secondary winding of the
ignition coil delivers the spark to the distributor to be sent to the spark
plugs. If it's bad, you'll get a weak spark or no spark at all.
To test
the secondary winding, attach test probes to terminal 15+ and the centre pole
(where the thick wire goes to the distributor). The resistance should be 2.4 to
3.5 kΩ. If it is out of range, toss the coil.
If
ignition coil is overheating and breaking down, causing misfiring and lack of
power, test the ignition switching function of the control unit (the
black box under the rear seat, otherwise known as the ECU).
Connect
the multimeter probes to terminals 15 (+) and 1 (-) on the ignition coil.
Disconnect
Hall Sender plug on distributor.
Have an
assistant switch the ignition ON.
Ground
the centre wire of hall sender plug for approximately 3 seconds. The displayed
voltage must increase briefly to approximately 4.5 volts.
If not,
replace control unit. (See Bentley manual 28.44).
(My ECU
failed this test – the symptoms were misfiring and backfiring after driving for
over 45 minutes. It was more noticeable when travelling uphill at highway
speeds. The coil was too hot to hold. I replaced the ECU and it solved the
problem.)
Engine earths; clean the connections on the braided wire between the engine and the
bodywork with emery paper and a wire brush. According to an NRMA survey, poor
earths are the most common cause of engine breakdowns. Also check that the
earth connection on the battery is clean.
Check all electrical connections, check wires for cracked or melted insulation or
broken wires or connections which can cause an intermittent problem. The
fragile connector on the hall sender is often damaged.
Check relays and connections in the engine compartment. Always carry spare relays
and replace if in doubt.
Ignition leads; test leads for continuity and damage.
Suppressor plug lead to distributor cap connectors 0.6 to 1.4 kΩ
Spark plug connectors 4 to 6 kΩ. Check that they are dry and undamaged
and tightly connected to the ignition leads.
Rotor 0.6-1.4
kΩ. Check for damage. Always carry a spare and replace if in doubt.
Distributor cap; check for cracks and carbon tracking, and inspect the spring-loaded
graphite centre-post as it may wear or break. Always carry a spare and replace
if in doubt.
Spark Plugs; Check that the correct spark plugs are fitted, and inspect the
condition of the ceramic insulator, the integrity of the electrodes, and the
spark plug gaps.
It is
best to check all of these items in the comfort of your shed at least once a
year (or before any major expedition) along with changing oils, fluids and
filters, checking all the sensors and adjustments as per the Bentley manual,
and lubricating everything that moves.
It is fun
and educational to remove the engine lid and run the engine on a dark night.
Stray sparks, luminescence and lightning bolts can be very illuminating.
If an
ignition coil fails completely, it will make no spark at all. But if it is
performing below par, it can make a weak spark that can cause the van to run
badly.
Symptoms
can include partial loss of power, erratic idle, stumble and miss on
acceleration from low revs, flat spots, missing under load, and cutting out.
Symptoms may only present themselves (or get worse) as the engine heats up (and
the coil is too hot to touch). If the engine stops, or fails to start when hot,
it may restart after the coil has cooled down.
Although a
coil passes all tests with the ohm-meter it can still deteriorate when hot, due
to degradation of internal insulation.
If
planning a desert expedition, fit a new coil and carry the old one for a spare.
Problems
with a weak coil will be exacerbated by poor maintenance of other ignition
components such as faulty or incorrect spark plugs, excessive spark plug gaps,
faulty plug leads or connectors, or loose or dirty electrical connections.
Broken wires are not always obvious, causing intermittent faults. Old and cracked
distributor caps and rotor buttons, and poor earth connections from the engine
to the bodywork can be problematic. A combination of any or all of theses
conditions can contribute to the early demise of a coil.
I once
tested three used VW coils in search of a good one. All would make the engine
run, but none of them were up to spec. The purchase of a new coil made a
noticeable difference.
The primary winding of the ignition coil is
the first to receive voltage from the battery when the ignition switch is
turned on, via terminal 15 (+).
Using a
multimeter, place the probes on the small outside wires (terminals 15(+) and
1(-). If the primary resistance between the two is 0.5 to 0.8Ω, the primary
winding is ok and you can go on to the secondary test. If it is out of spec,
replace the coil with the spare that you always carry under the seat.
The
secondary winding of the ignition coil delivers the spark to the distributor to
be sent to the spark plugs. If it's bad, you'll get a weak spark or no spark at
all.
To test
the secondary winding, attach test probes to terminal 15+ and the centre pole
(where the thick wire goes to the distributor). The resistance should be 2.4 to
3.5 kΩ. If it is out of range, toss the coil.
If
ignition coil is overheating and breaking down, causing misfiring and lack of
power, test the ignition switching function of the control unit (the
black box under the rear seat, otherwise known as the ECU).
To test
the ECU; (See Bentley manual 28.44).
Connect
the multimeter probes to terminals 15 (+) and 1 (-) on the ignition coil.
Disconnect
Hall Sender plug on distributor.
Have an
assistant switch the ignition ON.
Ground the
centre wire of hall sender plug for approximately 3 seconds. The displayed
voltage must increase briefly to approximately 4.5 volts.
If not,
replace control unit.
(My ECU
failed this test – the symptoms were misfiring and backfiring after driving for
over 45 minutes. It was more noticeable when travelling uphill at highway
speeds. The coil was too hot to hold. I replaced the ECU and it solved the
problem.)
Other things to
check;
Engine earths; clean the connections on the
braided wire between the engine and the bodywork with emery paper and a wire
brush. According to an NRMA survey, poor earths are the most common cause of
engine breakdowns. Also check that the earth connection on the battery is
clean. I generally add another earth wire to the cylinder head on the driver’s
side, as it lacks a good track to earth due to the fact it is insulated by
gaskets and sealant from the rest of the engine.
Check all electrical connections, check wires for cracked or melted
insulation, broken wires or connections which can cause an intermittent
problem. The fragile connector on the hall sender is often damaged.
Check relays and connections in the engine
compartment. Always carry spare relays and replace if in doubt.
Ignition leads; test leads for continuity and
damage.
Suppressor plug lead
to distributor cap connectors;
0.6 to 1.4 kΩ
Spark plug connectors; 4 to 6 kΩ. Check that they are dry
and undamaged and tightly connected to the ignition leads.
Rotor; 0.6-1.4 kΩ. Check for damage.
Always carry a spare and replace if in doubt.
Distributor cap; check for cracks and carbon
tracking, and inspect the spring-loaded graphite centre-post as it may wear or
break. Always carry a spare and replace if in doubt.
Spark Plugs; Check that the correct spark
plugs are fitted, and inspect the condition of the ceramic insulator, the
integrity of the electrodes, and the spark plug gaps. Bosch W7CC or Beru
14-7-CU are recommended.
It is best
to check all of these items in the comfort of your shed at least once a year
(or before an expedition) along with changing oils, fluids and filters,
checking all the sensors and adjustments as per the Bentley manual, and
lubricating everything that moves.
It is
educational to remove the engine lid and run the engine on a dark night. Stray
sparks, luminescence and lightning bolts can be very illuminating.
Searching for a substitute coil;
A canister
coil for suppressed electronic ignition systems is used. It is not the same as
that used on the VW air-cooled engines with points ignition. It has a female king-post
with a male prong for 6mm high-tension lead to the distributor. (Some
non-genuine coils will accept a 7mm HT lead. The metal ‘wings’ on the HT
end-plug needs to be bent outward slightly for a good fit).
The
original coil was manufactured by Bosch and carried VW part number 211 905 115D, and carried a green label.
They were fitted to all VW DJ & MV transporters from 1984-92. Versions of
this coil are still readily available from around $35 - $50[i]
from most VW parts suppliers. (Some early models had the 211 905 115 B coil
with .52Ω to .76Ω primary and 2.4Ω to 3.5Ω secondary resistance)
The Bosch
p/n was 0221 122 350, (now
discontinued and replaced with 0221 122
349). I priced one of the latter at Autobarn for $160.[ii]
Discussion on other websites indicates that Bosch components are rarely made in
Germany
nowadays. The quality of the Spanish and Mexican units are not as good as the
German, but far superior to the cheap Chinese clones. Google “bosch ignition
coil 0221 122 349.” I found them on Ebay for $106 to $120 in July 2016.
If searching
for parts from a wrecking yard, check out VW Golf, Passat, Polo and Jetta
models of similar vintage. They can also be found on various Audi 80/90/100,
BMW 316, 318 & 525, Saab 900, Holden Calibra, and Volvo 240, 740, 760 &
940 models in the same era.
Some
engines (primarily imports with DF, DG, SP and DJ prefix) were fitted with a
coil with a grey label – 191 905 115 A/B/C with .6Ω to .8Ω primary and 6.9Ω to
8.5Ω secondary resistance)
Other brands claim to be an
identical replacement;[iii]
Fuel Miser
CC501 ($46 - 110)[iv] commonly
available in Australian stores.
RAE C285 commonly
available in Australian stores.
Beru ZS123
or ZS 124 (both listed for all VW T3 1.9 & 2.1 1984-91).
NGK U180
48343
IGC 137
(around $100[v])
Topran 103
240 (sold through some outlets as 211 905 115D) $49[vi]
I have tried
the Topran, and it let me down on the first trip – luckily I still had the
original under the seat!
A search
of the internet reveals other alternatives; Automega, Bremi (11906 & 11822),
BBT (ICO 3105), Beru (0040100124), Bougicord (155084), Facet (96206), Era (880030),
JP (905210001), Mapco, Pex, Quinton Hazell, Standard, Vemo (V10700072 &
V10700052), and several Chinese manufacturers – Frey, Microne, Hongsheng and
Jitai.
[ii]
May 2016. Also available on the usual US, UK and Euro websites.
[iii]
Please double-check before
ordering.
[iv]
Repco $46, Auto One $110, May
2016
[vi]
VWHeritage Australia May 2016. (I fitted one
in April, it failed on the first long trip).